Variable capacity pump



July 21, 1959 G. T. sHoosMl'rH 2,895,423

' VARIABLE 'CAPACITY'PUMP Filed Aug. 2s. 1956 A ttarne United StatesPatent C) VARIABLE CAPACITY PUMP Guy T. Shoosmith,` St. Mary Bourne,England, assigner to Plenty and Son Limited, Newbury, EnglandApplication August 28, 1956, Serial No. 606,771 Claims priority,application Great Britain August 31, 1955 3 Claims. (Cl. 10S-120) Thisinvention relates to variable capacity pumps of the sliding vane type.

Because of the alternating pressure and suction in the pumping spaces orchambers of such pumps, the sliding block which bounds those chambersand the eccentricity of which relatively to the rotor governs the strokeof the vanes and consequently the capacity of the pump is subjected tocyclic pulsations. These are transmitted to the screw control gearthrough which the sliding block is adjusted. In pumps of small capacityoperating at low pressure, the pulsations are of small magnitude and ofno great consequence. In pumps of large capacity operating at highpressure, however, they are large. For example, in a pump designed todeliver 400 tons an hour at 300 lb. per sq. in., they can be of theorder of 40 tons and the screw control gear has to be designed to enableit to be operated when subjected to an alternating force of 40 tonshaving a periodicity of four times the shaft revolu` tions.

It is therefore an object of the invention to -relieve the screw controlgear of all or a substantial part of the loading resulting from thecyclic pulsations so that it does not have to be made cumbersome,expensive and heavy to operate.

Another object is to provide a variable-capacity pump wherein the cyclicpulsations of the sliding block are liquid-damped.

A further object of the invention is to provide an hydraulic dampingsystem for the sliding block of a variable capacity pump which is simpleand comparatively inexpensive.

Yet another object is to prove an hydraulic damping system for thesliding block of a variable capacity pump which does not hindervariation of the capacity of the pump when such variation is desired bythe pump operator.

According to the invention, the sliding block is made a good sliding fitin the body of the pump so that on either side of it there are sealedchambers. These chambers are lled with a liquid (generally oil), and areinterconnected by a passage containing an adjustable throttle valve. Theliquid thereby serves to damp out the cyclic pulsations of the slidingblock.

In order that the invention may be thoroughly understood, avariable-capacity pump in accordance with it will now be described withreference to the accompanying drawing which shows the pump in partialcross-section with parts broken away for the sake of clarity.

It will be seen that the pump comprises a pump body or housing 8 havinga suction passage or inlet 9 and a delivery passage or outlet 11. Withinthe housing 8 there is mounted for rotation a rotor shaft 10 having apair of slots 12 lying on ydiameters of the shaft in which are mountedto slide a pair of vanes 14. The ends of the vanes 14 bear on planesurfaces 16 formed on the interior of the rotor proper shown at 18.

The rotor 18 is mounted Within a bearing sleeve 20 carried by a. cage orsliding block 22 mounted for rec- 2,895,423 Patented July 21, 1959 licetilinear, vertical movement along the slides 23 formed on the inside ofthe pump housing 8. The sliding block 22 has straight outer surfaceswhich bear on the slides 23 and is a good sliding fit. As will be seen,vertical displacement of the sliding block 22 varies the extent of thesliding movement of the vanes 14 and, therefore, the capacity of thepump. This displacement of the cage is effected through acapacity-adjusting control spindle 24 which extends up through the pumphousing and which can be rotated by means of the screw-wheel 25.

Above and below the sliding block 22 there are formed two sealedchambers 26, 28 each of which is bounded on one of its sides by thesliding block. These chambers 26, 28 are inter-connected by a pipe 30which is provided with an adjustable throttle valve 32 and, at itshighest point, with an air cock 34. The two chambers 26, 28 and theinterconnecting pipe 30 are filled with a liquid, usually oil. As willbe seen the chambers 26, 28 are entirely separated from the suction anddelivery passages 9, 11 by mating portions 27, 29 of the sliding block22 and the pump housing 8.

Thus, by adjustment of the valve 32, the pulsations transmitted throughthe sliding block 22 to the liquid can be damped out either entirely orto any desired extent, and the screw control gear 24, 25 can thereby berelieved of any undesirable loading.

By closing the valve 32 altogether, a complete hydraulic lock can beproduced and the pump will normally be operated in that condition whenworking on a fixed stroke. When the stroke of the pump is to be altered,the valve 32 is opened to some extent so that liquid can be transferredfrom one chamber to the other but so that the cyclic vibrations aredamped out or reduced so as not to interfere with the operation of thescrew control gear.

It is of importance that the hydraulic circuit comprising the twochambers 26, 28 and the passage 30 connecting them should be free fromair and this is the reason why an air cock 34 is provided at the highestpoint in the circuit. As the liquid may contain entrained air, the aircock 34 may have to be left open for a considerable period before allthe air is expelled.

I claim:

1. A variable capacity pump comprising a hollow pfump body, a suctionpassage and a delivery passage in said pump body, a sliding blockslidably mounted within said pump body, a rotor shaft rotatable withinsaid pump body, means mechanically connected to said sliding block andarranged externally of said pump body on an upper portion thereof forslidably moving said sliding block whereby to alter the relativepositions of said sliding block and said rotor shaft, sealed chambers oneither side of said sliding block Within said pump body, each of saidsealed chambers being bounded on one side by said sliding block,portions of 'said pump body and said sliding block sealingly preventingat all times communication between said sealed chambers and said suctionpassage and said delivery passage, a passage inter-connecting saidsealed chambers, a throttle valve in said inter-connecting passage,valve adjusting means independent of said means rnechanically connectedto said sliding block for adjustably moving said throttle valve into aplurality of throttling positions and into one position wherein saidvalve closes said interconnecting passage, said valve adjusting meansbeing adapted to maintain said throttle valve fixed in any position towhich said valve is moved irrespective of variations in the fluidpressures in said pump body, said sealed chambers and saidinter-connecting passage being lilled with liquid whereby cyclicpulsations of said sliding block are damped out.

2. A variable capacity pump comprising a hollow pump body, a suctionpassage and a delivery passage in said 3 pump body, 'a rotor shaftwithin said pump body, slots in `said rotor shaft, sliding vanes,slidably mounted within said slots, a sliding block slidably mountedwithin said pump body, a rotor body rotatably mounted within saidsliding body, bearing surfaces internallyfdisposed on 'sai'd rotor body,bearing :surfaces fon the 'ends lof "said 'sliding vanes :in slidinglengagement with said bearing surfaces of said rotor body, 4meansmechanicallyconnected to said sliding block and arranged externally of'said pump body on an upper portion thereof for slidably movingsaidsliding :block whereby to alter fthe relative positions of said slidingblock-and said irotor shaft, a^sealed chamber immediately above saidrsliding block and bounded on-one side by said sliding block Awherebymovement of Asaidblock varies the capacity of said chamber, a secondsealed chamber immediately below said ysliding block and bounded'on oneside by said sliding block whereby movement of Vsaid lblock varies the:capacity of said second chamberrinversely-as the capacity of saidErst-mentioned sealed chamber is varied, Aportions of said pump bodyvand said sliding block'matingwith each other whereby to separate at all.times said sealedl chambers from said suction passage and said deliverypassage, .a tubeconnecting said sealed chambers together, a throttlevalve in said rtube, valve adjusting means independent of said meansmechanically connected to said sliding block 'for adjustably moving saidthrottle valve into a plurality of throttling positions and into oneposition wherein said valve closes said tube, said valve-adjusting meansbeing adapted .to maintain said throttle valve xed in any position towhich said valve is moved irrespective of variations in the fluidpressures in said pump body, an air-cock in said tube and located at thehighest point thereof, 'said sealed chambers and said connecting tubebeing filled with oil whereby cyclic pulsations of said sliding blockare damped out.

3. A variable capacity pump as -claimed in claim 2 wherein saidvalve-adjusting means are operable solely through a manually-actuated:member :located lexternally of said pump body.

References Cited in the file of this Apatent UNITED STATES PATENTS1,370,810 Hansen Mar. 8, 1921 1,467,837 Colebrook Sept. 11, 19232,296,876 Samiranet al Sept. 29, 1942 2,330,558 -Curtis Sept. '28, 19432,678,607 Huferd et al. May `l8, 1954 2,684,636 Heldenbrand J uly 27,l1954 2,724,339 'OConnoret al Nov. 22, 1955 2,823,614 Lapsley Feb. 18,1958 FOREIGN yPATENTS 414,752 "Great :Britain Aug. 9, 1934 609,906AGreatBritain Oct. l8, 1948

